MEMORANDUM

TO: Docket ID No. EPA-HQ-OAR-2015-0764

FROM: Alexis McKittrick and Mark de Figueiredo, EPA/CCD

DATE: January 21, 2016

SUBJECT: Duration of Leaks in Time Variab le of Equation W-30 of Subpart W

The U.S. Environmental Protection Agency (E PA) is proposing revisions to 40 CFR part 98, subpart W (hereafter referred to as “subpart W”) in order to align subpart W with proposed new source performance standards (NSPS) for th e oil and gas source category (40 CFR part 60, subpart OOOOa; hereafter referred to as “NSPS subpart OOOOa”) (see 77 FR 49542; September 18, 2015). Specifically, the EPA is proposing to a dd the optical gas imaging (OGI) monitoring method proposed in NSPS subpart OOOOa to subpart W. In addition, the EPA is proposing to add new leaker emission factors in subpart W for industry segments and/or components that currently do not have leaker emi ssion factors so that the new m onitoring data can be used when estimating greenhouse gas emissions in subpart W. If finalized, proposed NSPS subpart OOOOa would require facilities also reporting under su bpart W to perform fugitive emission monitoring separate from the requirements currently in subp art W and repair leaking equipment. Facilities that would be newly subject to proposed N SPS subpart OOOOa would be required to do an initial monitoring survey, conduct a second mon itoring survey one month later, then begin conducting semi-annual surveys.

Equation W-30 of subpart W is used to calcu late equipment leak emissions using leak detection survey data, leaker emissi on factors, and a time variable, T p,z , to account for the time an equipment component was leaking. This time variable is curren tly defined at 40 CFR 98.233(q) as follows:

The total time the surveyed component “z”, component type “p”, was assumed to be leaking and operational, inhours. If one leak detecti on survey is conducted in the calendar year, assume the component wa s leaking for the entire calendar year, accounting for time the component was not operational ( i.e. , not operating under pressure) using engineering estimate based on best available data. If multiple leak detection surveys are conducte d in the calendar year, a ssume that the component found to be leaking has b een leaking since the prev ious survey (if not found leaking in the previous survey) or the beginning of the calendar year (if it was found leaking in the previous survey), accounting for time the component was not operational using engineering estimate base d on best available data. For the last leak detection survey in the calendar y ear, assume that all leaking components2 continue to leak until the end of the calendar year, accounting for time the component was not operational using engine ering estimate based on best available
data.

The current language for the definition of the time variable specifically considers a first leak survey and a last leak survey in the year, but does not provide specif ic language with respect to the duration of any “intermediate” survey conducted between the fi rst and last survey. Therefore, the EPA is proposing to amend the definition of the time variable, T p,z , of Equation W-30 to clarify what reporters should do if more than two leak surveys are conducted in a year.

In addition, in response to comments as part of the 2010 subpart W final rule, the EPA
further clarified how the time variab le is intended to be applied:

...EPA recognizes the commenter’s concer n that assuming a leak duration of 365 days may overestimate emissions. Conversely, there will be leaks that start after a leak survey is conducted and therefore an underestimation may occur as well. Regardless, in today’s final rule, EPA allows reporters the option to perform subsequent facility-wide leak detection surveys and to adjust their emissions to account for components that are subsequently found to be leaking or not leaking, respectively. EPA emphasizes that adjustme nt of emissions is not allowed based on repair records alone. Reporters must assume that a leaking component has been leaking starting from the beginning of the calendar year. In addition, if only one leak detection survey is conducted during the calendar year, the reporter must
assume that the duration of the leak is 365 days unless the leak is fixed and a subsequent official leak de tection survey is conducte d for an entire facility proving that the leak and othe rs were repaired. A goal with leak detection is to get a facility wide snapshot of equipment l eak emissions. If a re porter finds certain components leaking during a specific surv ey they are usua lly not addressed immediately. During the time leaks are be ing addressed, other leaks will appear which only subsequent facility wide leak detection surveys will ascertain. 1

In other words, subpart W specifi es that any leak that is iden tified during a leak detection survey is assumed to continue to leak until the ne xt complete survey indicating the leak has been repaired (or until the end of the reporting year, if identified during the last survey conducted in a reporting year).

1 U.S. Environmental Protection Agency. Mandatory Greenhouse Gas Reporting Rule Subpart W – Petroleum and Natural Gas: EPA’s Respon se to Public Comments . November 2010. Docket Item No. EPA-HQ-OAR-2009-0923- 3608. Response to Comment Number EPA-HQ-OAR-2009-0923-1014-9, pp. 1281–1282.3 As the proposed NSPS subpart OOOOa require s repair of fugitiv e leaks, the EPA
considered the need to further amend the definition of the time variable, T p,z , of Equation W-30 beyond the proposed clarification discusse d above to account for these repairs.

Option 1 (Current Requirement) . As stated above, currently insubpart W, any leak that is identified during a leak detection survey is as sumed to have been leaking since the previous complete leak survey or the beginning of the re porting year, whichever is more recent, and the
leak is assumed to continue to leak until the ne xt complete survey indicating the leak has been repaired (or until the end of the reporting year, if identified during the last survey conducted in a reporting year).

Option 2 . Consider each complete leak detection survey independently when multiple complete surveys are conducted in a reporting year. For the last complete survey of the reporting year, the leak duration is from the previous l eak detection survey until the end of the reporting year, just as currently required. However, for th e first complete survey in a reporting year, the leak duration is from the start of the reporting year until the date of the first leak survey (instead of being considered to be leaking up to the next leak survey). The leak duration for an intermediate leak detection survey is the time from the date of the previous leak detection survey through the date of that intermediate leak detection survey (inst ead of being considered to be leaking up to the next leak survey).

Option 3 . Allow remonitoring of individual component s to count as a leak survey for that component for the purposes of th e time period considered in T p,z . Assume the leak duration begins on January 1 of the reporting year or on the date of the previ ous non-leaking survey (whichever is later) and continues until the next su rvey of that component or until the end of the reporting year (whichever is earlier). In this option, the component is assumed to leak until December 31 only when the component is not repair ed. Otherwise, the leak period ends with the remonitoring of the repaired component.

Option 4 . Allow remonitoring of individual components to count as a survey, as in Option 3, but do not confine the duration of a leak to a reporting year. For example, if a leak is not repaired in reporting year (RY) 2016, than that leak is assumed to continue into RY2017. Similarly, if the first survey c onducted in RY2017 identifies a leak, then that leak is assumed to occur from the last monitoring event in RY2016. Th e reporter would then n eed to attribute the duration of each leak attributable to a given repo rting year (for leaks sp anning reporting years) in
order to determine the value for T p,z of Equation W-30 for that reporting year.

In order to provide consistency and clarity for subpart W reporters in the proposed rule amendments, the EPA chose Option 1, which retain s the existing requirements for application of time variable, T p,z , of Equation W-30.